Holograms are the perfect practical example of the "wave" nature of light.While we often think of light in terms of "photons," light is also a "wave." The different colors of light that we see are actually different wavelengths of the light: red is longer, blue is shorter, and green is in the middle.
Laser light is used for holograms because it is a very pure source of light (only one color, or wavelength) with very orderly waves . When two beams of laser light come together, they form an interference pattern . This is the most basic form of a hologram.
Imagine throwing a rock into a quiet lake. The ripple pattern is like the waves that come from a laser. If you throw two rocks into the water, the two wave patterns will collide in the middle, creating some areas that have waves twice as big and some areas where the waves cancel each other out. This is interference.
To make a hologram , laser light is split into two different beams. One is reflected off of an object and then scatters to the film, while the other beam goes directly to the film. The two beams meet at the film causing an interference pattern of microscopic bright and dark lines. The film captures this pattern, which is the hologram.
A regular photograph is only two-dimensional (2D) because it only records the INTENSITY of the light hitting the film, recording shades of brightness and darkness. A hologram is three-dimensional (3D) because it records both the INTENSITY and the DIRECTION of the light that hits the film. This additional information is recorded in the interference pattern, and allows you to "look around" the recorded object as if it were really there.
To view the hologram after it is developed (if you are using the Litiholo "Instant Hologram" Film, there is no developing necessary), it is placed back in its original position and illuminated with only one beam coming directly from the laser. The recorded holographic interference pattern will now diffract the laser light passing through it, creating a 3D image of the original object as if it was still there.
Diffraction is the bending of light due to a pattern of closely spaced lines. If you look at the bottom of a CD or DVD disk, you will see a rainbow of colors. This is because the tracks on the CD create microscopic lines that bend (or diffract) the light into.